(1) Field of the Invention
This invention pertains to the conversion of hydrocarbons especially the dehydrogenation of dehydrogenatable hydrocarbons, in the presence of a heterogeneous catalyst composite. Dehydrogenatable hydrocarbons contain at least two non-aromatic adjacent carbon atoms having one or two carbon-carbon bonds in common, each carbon atom of the pair having at least one hydrogen atom bonded to it. A heterogeneous catalyst is one which is in a phase different from the phase or phases of the reactants it catalyzes, for example, a solid catalyst which catalyzes liquid or gaseous reactants.
Dehydrogenating hydrocarbons is an important commercial process because of the great demand for dehydrogenated hydrocarbons especially olefins, as raw materials for the manufacture of various chemical products such as detergents, high octane gasolines, pharmaceuticals, plastics, synthetic rubbers, and other well-known products. In a commercial dehydrogenation process it is generally desired to dehydrogenate the hydrocarbon feedstock with little or no simultaneous cracking or isomerization of it. Preferably, the isomerization activity of dehydrogenation catalysts is maintained at less than 2 mol % of the feedstock, measured as the number of mols of isomerized hydrocarbons in the product relative to the feedstock. Preferably, the cracking activity of dehydrogenation catalysts is maintained at less than 10 mol % of the feedstock, measured as the number of mols of cracked hydrocarbons in the product relative to a feedstock of pure isobutane. One example of a dehydrogenation process is dehydrogenating isobutane to produce isobutylene which can be used to make, for example, tackifying agents for adhesives, viscosity-index additives for motor oils and impact-resistant and anti-oxidant additives for plastics.
(2) Description of the Prior Art
It is well known to catalyze the conversion of liquid or gaseous hydrocarbons with solid catalysts comprising platinum group metals. For example, U.S. Pat. Nos. 2,479,109 and 2,479,110 disclose a catalyst comprising platinum on alumina with combined halogen for catalyzing reforming, hydrogenating, hydrocracking, oxidizing and dehydrogenating reactions. The term "reforming" in these patents means simultaneously dehydrogenating, isomerizing, cyclizing and cracking a gasoline feedstock. The combined halogen component of this catalyst contributes to a controlled type of cracking activity. For reforming applications the halogen content is preferably maintained below about 8 weight % of the alumina to avoid excessive side reactions, including cracking reactions, which result in excessive gas formation and low liquid volume yield of reformed products.
U.S. Pat. No. 2,602,772 discloses converting hydrocarbons, especially reforming and hydrocracking hydrocarbons, with a catalyst comprising platinum, not more than 1 weight % of an oxide of an alkaline earth metal or magnesium and from about 0.1 to about 8 weight % combined halogen on alumina. According to this patent catalysts containing an alkaline earth metal or magnesium oxide produced less carbon, or coke, after 3 days of reforming operations. The halogen content for catalysts of this patent is from 0.3 to 3 weight %, preferably between 0.6 and 2.3 weight %.
U.S. Pat. No. 2,930,763 discloses a two-step process for reforming hydrocarbons. In the first step a hydrocarbon fraction containing unsaturated compounds and/or nitrogen, sulfur or oxygen compounds is contacted with hydrogen in the presence of a catalyst comprising platinum and an alkali metal component on alumina to hydrogenate and saturate the unsaturated compounds and/or reduce the nitrogen, sulfur or oxygen content of the hydrocarbon fraction. In the second step of this process the treated hydrocarbon fraction from the first step is contacted at reforming conditions with a conventional reforming catalyst comprising platinum and combined halogen on alumina. Optionally the catalyst utilized in the first step may contain halogen. A catalyst consisting essentially of alumina, from about 0.01% to about 1% by weight of platinum, from about 0.1% to about 1% by weight of combined halogen, and from about 0.01% to about 1% by weight of an alkali metal is recited in claim 2 of this patent.
U.S. Pat. No. 3,531,543 discloses dehydrogenating hydrocarbons with a catalyst comprising platinum, tin and neutralized metal oxide supports. The preferred supports are oxide materials whose intrinsic acidity is substantially reutralized by an alkali or alkaline earth metal component. Pure alumina, for example, has such intrinsic adicity. (cf. Pines and Haag, Journal of the American Chemical Society, 82,2471 (1960). Evidence of this acidity is that alumina catalyzes the skeletal isomerization of olefins, dehydrates alcohols and strongly chemisorbs amines. Also, with increasing amounts of alkali present there is a parallel decrease in these acidic alumina properties. Preferably the support of this patent is a non-acidic lithiated alumina. Perferably, the catalysts of this patent are prepared from halogen free compounds. Compounds containing halogen may be used provided halogen is efficiently removed from the catalyst.
U.S. Pat. No. 3,647,680 discloses a continuous moving bed reforming-regeneration process utilizing a catalyst comprising a platinum group metal, combined halogen and alumina. The catalyst may also include a promoter, such as rhenium, for example. The catalyst is continuously cycled between the reforming reactor section and catalyst regeneration section to maintain catalyst activity at a predetermined high level without the removal of any reactor from the process stream. The catalyst regeneration section includes a carbon burn-off zone, a chlorination zone and a drying zone. A catalyst reducing zone is located immediately upstream of the reforming reactor section. In the chlorination zone, the catalyst is contacted with about a 2:1 mol ratio of steam and chlorine.
U.S. Pat. No. 3,652,231 discloses a reforming catalyst regeneration apparatus suitable for use in the regeneration section of the process disclosed in U.S. Pat. No. 3,647,680 discussed above. This apparatus comprises a carbon burn-off section, a halogen section and a drying section.
U.S. Pat. No. 3,745,112 discloses a catalyst for reforming hydrocarbons with comprises a platinum group component, a tin component and a halogen component with a porous support material. This patent discloses also that a platinum-tin-alkali or alkaline earth composite is a particularly effective catalyst for dehydrogenating hydrocarbons. In the dehydrogenation catalyst of this patent the alkali or alkaline earth component is added and the amount of halogen, if not entirely eliminated, is minimized in order to minimize or neutralize, according to the understanding of the art, the acidic functions of the alumina and halogen components which tend to promote cracking and isomerization reactions.
U.S. Pat. No. 3,892,657 discloses that indium is a good promoter for platinum group-containing catalysts when the atomic ratio of indium to platinum is from about 0.1:1 to about 1:1. This patent discloses also that a Group IVA component selected from the group of germanium, tin, and lead can be added to the acidic form of the indium-containing catalysts for reforming applications. The acidic form of this catalyst, then, comprises a platinum group component, a Group IVA component, an indium component, a halogen component and a porous support material. The acidic catalyst contains up to about 3.5 weight % halogen for reforming applications and up to about 10 weight % halogen for isomerization and cracking applications. In the dehydrogenation catalyst of this patent the alkali or alkaline earth component is added, however, and the halogen content is maintained at the lowest possible value (about 0.1 weight %).
U.S. Pat. No. 3,909,451 discloses a new method for making a dehydrogenation catalyst comprising a platinum component, a tin component and an alkali or alkaline earth component. In Example V this patent discloses a platinum, tin and potassium composition comprising less than 0.2 wt. % combined chloride.
U.S. Pat. No. 3,978,150 discloses a continuous moving bed dehydrogenation-regeneration process utilizing, preferably, a catalyst comprising chromium, vanadium or molybdenum, such as alumina promoted with chromium oxide. The catalyst regeneration section in this process comprises a carbon burn-off zone and a catalyst reducing zone, which is preferably designed in accordance with the teachings of U.S. Pat. No. 3,652,231 discussed above, but without the halogenation zone.
U.S. Pat. Nos. 4,329,258 and 4,363,721 disclose a catalyst comprising a platinum group metal, tin, an alkali or alkaline earth metal and combined halogen with a refractory oxide-mineral support. The atomic ratio of alkali or alkaline earth metal to platinum group metal for catalysts of these patents is from 0.2 to 10. These patentees discovered that parts-per-million quantities of alkali or alkaline earth component added to catalysts containing a platinum group metal and tin helped increase the C.sub.5+ yield in a reforming process.
British Patent 1 499 297 discloses a dehydrogenation catalyst comprising platinum, at least one of the elements gallium, indium and thallium, and an alkali metal, especially lithium or potassium, with alumina as the carrier material. The catalysts of this patent also contain halogen in an amount of from 0.01 to 0.1 weight %. The halogen content is purposely reduced to within this low weight % range in order to increase the selectivity and stability of the catalyst.
There is no prior art dehydrogenation process, then, wherein a used dehydrogenation catalyst comprising a platinum group component, an alkali or alkaline earth component and a porous support material is contacted in a catalyst regeneration zone with a halogen component to produce a regenerated catalyst containing added halogen component. Surprisingly, we have discovered that a regenerated dehydrogenation catalyst with added halogen component exhibits more activity and activity stability when it is reused to dehydrogenate hydrocarbons.